The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Generally, a bicycle frame includes a head tube, a seat tube, a top tube, a down tube, a seat stay and a chain stay.
An upper end portion of the head tube is connected with a steering handle portion and a lower end portion of the head tube is connected with a front wheel portion. An upper end portion of the seat tube is connected with a saddle portion and a lower portion of the seat tube is connected with a chain driver.
The top tube and the down tube connect and support the head tube and the seat tube, whereas the seat stay and the chain stay connect and support a rear wheel portion and the seat tube.
The bicycle frame may have both a top tube and a down tube, but in some cases, only one main tube may be connected between the head tube and the seat tube.
On the other hand, an electric bicycle is applied to a bicycle frame as a power source, and the bicycle frame is provided with a motor mounting portion for mounting the motor.
The engine mounting section is connected to the lower end portion of the main tube which is combined with the top tube and the down tube in the bicycle frame. The upper end portion of the main tube is connected to the head tube and the middle portion of the main tube is connected with the seat tube.
The seat tube is connected with the rear end portion of the chain stay, and the lower end portion of the seat tube and the front end portion of the chain stay are connected with the motor mounting portion.
As described above, the frame of the electric bicycle is made by manufacturing the motor mounting part according to the specification and shape of the motor, cutting the tube as the base material according to the required length, and welding the motor mounting part and the tube.
The motor is mounted on the motor mounting portion of the bicycle frame through the motor mounting bracket made of aluminum casting.
With this method, it may be difficult to automate the production of bicycle frames, so productivity may be deteriorated and production cost may increase.
Therefore, in recent years, research has been developed to improve the productivity of the frame by stamping the plate material to bond the bicycle frame to the left and right.
However, in the conventional art in which a bicycle frame with a motor mounting part is stamped, a frame is produced by a process using a stamping mold. Therefore, when the specification and shape of the motor are changed, a new stamping die must be manufactured so that the frame has a motor mounting portion corresponding to the specification and shape of the motor.